from __future__ import print_function

from math import ceil

try:
    xrange  # Python 2
except NameError:
    xrange = range  # Python 3


def diagonal_sum(n):
    total = 1

    for i in xrange(1, int(ceil(n / 2.0))):
        odd = 2 * i + 1
        even = 2 * i
        total = total + 4 * odd ** 2 - 6 * even

    return total


if __name__ == '__main__':
    import sys

    if len(sys.argv) == 1:
        print(diagonal_sum(1001))
    else:
        try:
            n = int(sys.argv[1])
            diagonal_sum(n)
        except ValueError:
            print('Invalid entry - please enter a number')
